The present invention relates to methods and apparatus for monitoring the operation of sucker-rod well pumping units, and more particularly to methods and apparatus for detecting fluid pound in wells employing sucker-rod pumping units.
Sucker-rod type pumping units are widely used in the petroleum industry in order to recover fluid from wells extending into subterranean formations. Such units include a sucker-rod string which extends into the well and means at the surface for an up and down movement of the rod string in order to operate a downhole pump. Typical of such units are the so called "beam-type" pumping units having the sucker-rod string suspended at the surface of the well from a structure consisting of a Samson post and a walking beam pivotally mounted on the Samson post. The sucker-rod string normally is connected at one end of the walking beam and the other end of the walking beam is connected to a prime mover such as a motor through a suitable crank and pitman connection. In this arrangement the walking beam and the sucker-rod string are driven in a reciprocal mode by the prime mover.
A variety of malfunctions such as worn pumps, broken sucker-rods, split tubing, and stuck pump valves can interrupt the pumping of fluid from a well. Such malfunctions can be caused by normal wear and tear on the equipment, by the nature of the fluid being pumped or they could be caused by abnormal pumping conditions.
One abnormal pumping condition which is fairly common is known as "fluid pound". Fluid pound occurs when the well is pumped-off, i.e., when fluid is withdrawn from the well at a rate greater than the rate at which fluid enters the well from the formation. When this occurs, the working well of the downhole pump is only partially filled during an upstroke of the plunger and on the down stroke the plunger strikes or "pounds" the fluid in the working barrel causing severe jarring of the entire pumping unit. This causes damage to the rod string and to the surface equipment and may lead to failure of the pumping unit.